DAYTIME MELATONIN ADMINISTRATION ENHANCES SLEEPINESS AND THETA ALPHA ACTIVITY IN THE WAKING EEG/

It is still controversial whether the pineal hormone melatonin can be characterized as a hypnotic. We therefore measured subjective sleepine ss and waking EEG power density in the range of 0.25-20 Hz after a sin gle dose of melatonin (5 mg). During an 8 h mini-constant routine prot ocol, melatonin administered in a double blind cross-over design to he althy young men at 1300 h or 1800 h increased subjective sleepiness, a s rated half-hourly on three different scales (Visual Analogue Scale, Akerstedt Sleepiness Symptoms Check List, Akerstedt Sleepiness Scale) and objective fatigue as evidenced by augmented waking EEG power densi ty in the theta/alpha range (5.25-9 Hz). The increase in subjective sl eepiness reached significance 40 min and 90 min after melatonin admini stration (at 1300 h and 1800 h, respectively) and lasted for 3 h (at 1 300 h) and 5 h (at 1800 h). The increase in the theta/alpha frequencie s of the waking EEG occurred immediately after melatonin ingestion and stayed significantly higher parallel to the higher sleepiness ratings . However, the EEG changes appeared before the subjective symptoms of sleepiness became manifest. There was a significant correlation betwee n salivary melatonin levels and the timing of increased subjective sle epiness. Melatonin had no effects on mood.